Apparatus and method for processing two-tone image data so as to smooth image and convert each image pixel into a plurality of pixels

ABSTRACT

An apparatus processes two-tone image data so as to magnify a relevant image and smooth a boundary line between a zone consisting of first-tone pixels of two-tone pixels constituting the relevant image and a zone consisting of second-tone pixels of the two-tone pixels. The apparatus is characterized in that the apparatus comprises a unit which, for each two-tone pixel of the two-tone pixels, determines a template pattern, from among a plurality of template patterns, as matching a pixel arrangement comprising pixels located around the each two-tone pixel; and a unit for converting the each two-tone pixel into either single multiple-tone pixel of plurality of multiple-tone pixels, the unit using a result of the determination performed by the unit for the converting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 08/379,945, filed Jan. 27, 1995, now U.S. Pat. No. 5,611,023 whichis a continuation-in-part application of U.S. application Ser. No.08/115,148, filed Sep. 2, 1993, now U.S. Pat. No. 5,574,833.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method forprocessing two-tone image data so as to smooth and magnify a relevantimage. The above-mentioned apparatus and method may be applied to animage processing apparatus such as a facsimile apparatus, a digitalduplicator having a facsimile function, a digital duplicator not havingthe facsimile function, a printer such as an optical printer such as alaser printer, and so forth. Data to be processed by the apparatus ormethod is, for example, data such as that received through the facsimilefunction. The above-mentioned smoothing of a relevant image is removingjaggies or aliasing from the relevant image. The jaggies or aliasingmeans "stairsteps" undesirably appearing in inclined lines and curves ofan image when the image is represented at a relatively low resolution.The stairsteps are a series of steps consisting of a line such as aboundary line between a zone consisting of white pixels and a zoneconsisting of black pixels in an image and are like steps of a stair.

2. Prior Art

A smoothing technique will now be described. The smoothing technique isused in processing given two-tone image data so as to magnify a relevantimage an integer number of times. In such processing, a group of pixelslocated around a relevant pixel in the image are used as data todetermine a manner in converting the relevant pixel into a plurality ofpixels. Hereinafter, converting each pixel into a plurality of pixelswill be referred to as magnifying the pixel. Further, an operation to beperformed on an image such that a number of pixels (dots) constitutingthe image is increased will be referred to as magnifying of the image.As a result of such magnifying, it is possible to smoothly interpolatebetween steps of the jaggies which appear as a result of the magnifying.In this technology, output data is also two-tone image data. Such atechnology has been made practicable in a facsimile apparatus incommercial use.

Another technique is for removing the jaggies applicable to a printer orthe like having a capability of printing in a multiple-tone printingmanner. The technique attempts to obtain high-quality images as a resultof converting pixels consisting of the jaggies in an image representedby two-tone image data into pixels represented by multiple-tone imagedata. A typical technique of the above-described technique was madepracticable as a Resolution Enhanced Technology (which will beabbreviated `RET`, hereinafter) of HP (Hewlett-Packard). Further,similar techniques have been made practicable by other printermanufacturers.

Recently, a product such as that having a block structure shown in FIG.1 has appeared on the market.

The product is a system having a printer 1, a scanner 2, and a modem 3so as to constitute a digital duplicator having a facsimile function.The system performs a digital duplicating function of reading in anoriginal image through the scanner 2 and printing out the thus-read-inimage through the printer 1. Latest digital duplicators have a functionof printing an image in the multiple-tone printing manner as mentionedabove. The digital duplicating function is an essential function of thesystem. Further, the system has a printer function of printing out adocument produced by a word processing function of a computer 4connected to the printer 1. The system further has a network function ofprinting out data obtained through a network 5 connected to theprinter 1. The network function also includes a function of transferringan image to the network 5, the image having been read in through thescanner 2. The system further has a scanner function of storing imagesobtained through the scanner 2 in a file 6 (a recording medium such asan optical disc having a huge data storing capacity) and thus forming adata base of the thus-stored images. The system further has a facsimilefunction of communicating facsimile images through a public line 7 whichconnects the modem 3 with a facsimile machine 8.

FIG. 2 shows magnifications required in magnifying one of threedifferent sorts of images, which have been transmitted through facsimiletransmission methods, so as to print out the image through one ofprinters having three different resolutions, 300 dpi, 400 dpi and 600dpi. In the leftmost column of FIG. 2, indicating resolutions offacsimile reception images, "8×3.85" means "8 (dots/mm)×3.85(lines/mm)"; "8×7.7" means "8 (dots/mm)×7.7 (lines/mm)"; and "16×15.4"means "16 (dots/mm)×15.4 (lines/mm)". Similarly, in FIG. 2, the printerresolutions of "300 dpi (12×12)", "400 dpi (16×16)" and "600 dpi(24×24)" mean "300 dpi (12 (dots/mm)×12 (lines/mm))", "400 dpi (16(dots/mm)×16 (lines/mm))" and "600 dpi (24 (dots/mm) ×24 (lines/mm))",respectively.

How FIG. 2 should be viewed will now be described. In an example, if animage of 8×7.7 (second or middle row of FIG. 2) which have beentransmitted through a facsimile transmission method is printed through aprinter having a resolution capability of 400 dpi (second or middlecolumn of FIG. 2), it is necessary to magnify the image twice in ahorizontal direction and twice in a vertical direction that is, 2×2times.

Why the magnifying is necessary will now be described. If image data ofthe image of 8 (dots/mm) ×7.7 (lines/mm) is used to print out the imagethrough the printer having the resolution capability of 400 dpi (16(dots/mm)×16 (lines/mm)), each of a horizontal dimension and a verticaldimension of a resulting image is approximately half of a respective oneof those of the original image. This is because a number of dots (8) perunit length in the horizontal direction of the original image is 1/2 ofa number of dots (16) per unit length in the horizontal direction of theresulting image, each dot of the original image corresponding to arespective dot of the resulting image. Similarly, a number of lines(7.7) per unit length in the vertical direction of the original image isapproximately 1/2 of a number of line (16) per unit length in thevertical direction of the resulting image, each line of the originalimage corresponding to a respective line of the resulting image. Inorder to maintain the dimensions between the original image and theresulting image, it is necessary to magnify, that is, to double thenumber of dots per unit length in the horizontal direction and to doublethe number of lines per unit length in the vertical direction of, theoriginal image, before the printing out of the resulting image.

There is demand for system to be devised which simultaneously has afunction of image magnifying such as that shown in FIG. 2 and also afunction of the above-mentioned RET on the same image data. This systemmagnifies an image, represented by two-tone image data obtained throughthe facsimile method, while smoothing the image.

In order to respond to the above-mentioned demand, a certain imageprocessing method may be contrived. The certain image processing methodis a method of processing an image represented by two-tone image dataand obtained through the facsimile method. The certain image processingmethod uses a conventional smoothing technique so that an operation ofthe above-mentioned smoothly interpolating method is performed togetherwith magnifying the image an appropriate number of times. Then, anoperation of the RET is performed on the magnified and smoothlyinterpolated image. Then, the image is printed out in the multiple-toneprinting manner.

However, in order to realize the above-described image processingmethod, it is necessary to use two separate ASICs (Application-SpecificIntegrated Circuits), specifically, for example, gate arrays, one forthe above-mentioned smoothly interpolating operation and the other forthe above-mentioned RET operation. Therefore, high costs are required torealize the method. Further, circuit design of the ASICs and/or otherperipheral circuits depend on a resolution of a printer which isprovided with the ASICs. Since the resolutions of printers are atvarious levels, it is required that the circuit design be performed invarious manners to match the resolutions of the particular printers.

Further, there may be some pixels unexpectedly left without havingundergone the smoothly interpolating operation in the smoothingtechnique for the two-tone image data. The RET operation may not have aneffect on the thus-left pixels. As a result, an image, having a part inwhich a printing quality is degraded, may be obtained. Why the REToperation may not have an effect on the thus-left pixels will now bedescribed. There may be a case where a stairstep part is present in aboundary line between a zone consisting of black pixels and a zoneconsisting of white pixels. In the stairstep part, a number of pixelsconstituting each one of the vertical step dimension and the horizontalstep dimension is equal to or larger than two. If an image includingsuch a stairstep part is simply magnified by a factor of 2 in both thehorizontal and vertical dimensions, the each one of the vertical stepdimension and the horizontal step dimension is equal to or larger thanfour. A possibility of such a stairstep part, having long stepdimensions, being appropriately smoothed due to the RET operation islow.

SUMMARY OF THE INVENTION

An object of the present invention is to ensure effective performance ofsmoothing and magnifying operations on two-tone image data which mayconsist of data obtained through a facsimile method. Thus, a highprinting quality is obtained in an image obtained as a result ofprinting out the image data which has undergone the performance of thesmoothing and magnifying operations. The above-mentioned printing-out isperformed through a printer having a capability of printing out an imagein the multiple tone printing manner. Further, not only can such a highprinting quality be obtained, but also costs required for this purposecan be reduced. Further, the high printing quality can be maintainedeven if the relevant printers have gamma characteristics different fromone another, even if environmental conditions are different amongparticular printing occasions, and even if characteristics of theprinter vary due to aging. The gamma characteristics are characteristicsindicating relationship between input image tone values andcorresponding output (printed-out) image tone values and are, ingeneral, not linear.

An apparatus for processing two-tone image data according to the presentinvention magnifies a relevant image and smoothes a boundary linebetween a zone consisting of first-tone pixels of two-tone pixelsconstituting said relevant image and a zone consisting of second-tonepixels of said two-tone pixels. The apparatus is characterized in thatsaid apparatus comprises:

means (22) which, for each two-tone pixel of said two-tone pixels,determines a template pattern, from among a plurality of templatepatterns, as matching a pixel arrangement comprising pixels locatedaround said each two-tone pixel; and

means (23) for converting said each two-tone pixel into a plurality ofmultiple-tone pixels, said means (23) using a result of thedetermination performed by said means (22) for the converting.

Thus, by using the template patterns, each two-tone pixel can be easilyand surely converted into the plurality of multiple-tone pixels.Further, by the conversion, the relevant image can be easily and surelymagnified and the boundary line can be easily and surely smoothed.Further, the resulting multiple-tone pixels will be used by a printerwhich has a capability of printing out a multiple-tone image. As aresult, a high-quality image is obtained economically.

According to another aspect of the present invention, said apparatusfurther comprises:

means (28) for determining a magnification according to which saidapparatus magnifies said relevant image;

said means (28), for the determining of the magnification, using imagedata which is received through a facsimile function and is used toobtain said two-tone image data.

Thereby, it is possible that the magnification is determined such that,with the magnification, an image magnifying operation being performedmatches a combination of a type and a transmission resolution mode of afacsimile transmitting apparatus and a resolution of a relevant printer.The relevant printer is used in printing out a resulting image using themultiple-tone pixels. The magnification is such as one of those shown inFIG. 2. The type and transmission resolution mode of the facsimiletransmitting apparatus can be detected using the image data which isreceived through the facsimile function.

According to another aspect of the present invention, said apparatusfurther comprises:

means (29) for transferring smoothly magnified pixel data to said means(23), which data is previously prepared for said magnification and isused for converting said each two-tone pixel into said plurality ofmultiple-tone pixels in said means (23).

Thereby, it is not necessary that various kinds of the smoothlymagnified pixel data prepared for all possible magnifications be storedin the means (23). Therefore, a memory capacity required in the means(23) can be reduced and thus a cost required for the means (23) can bereduced.

According to another aspect of the present invention, said apparatusfurther comprises:

means (30) for correcting said smoothly magnified pixel data so as toeliminate a difference between ideal printing-out characteristics andactual printing-out characteristics.

This correction may be performed based on gamma characteristics of therelevant printer, environment variation such as ambient temperaturevariation, characteristics variation of a photosensitive substance drumand so forth in the printer due to aging thereof. As a result, it ispossible that a high-quality printed-out image is always obtained, whichimage has optimum tone characteristics. This is achieved by eliminatingeffects caused the gamma characteristics of the relevant printer,environment variation such as ambient temperature variation,characteristics variation of a photosensitive substance drum and soforth in the printer due to aging thereof.

A method for processing two-tone image data according to another aspectof the present invention is characterized in that

said method comprises steps of:

(a) determining, for each two-tone pixel of said two-tone pixels, atemplate pattern, from among a plurality of template patterns, asmatching a pixel arrangement comprising pixels located around said eachtwo-tone pixel; and

(b) converting said each two-tone pixel into multiple-tone pixels, saidstep (b) using a result of the determination performed by said means(22) for the converting.

Further, said step (b) further comprises steps of:

(b-1) converting said each two-tone pixel into a two-tone dot group;

(b-2) dividing said dot group into either a single division or aplurality of divisions; and

(b-3) averaging tones of dots constituting appropriate one of saidsingle division or said plurality of divisions, a result of theaveraging constituting tones of said multiple-tone pixels.

Further, said method further comprises steps of:

(c) classifying said plurality of template patterns into a first groupof patterns, a second group of patterns and a third group of patterns;

said first group of patterns being used to detect whether said each twotone-pixel is one not to be converted into the multiple-tone pixels;

said second group of patterns being used to detect whether said each twotone-pixel is one not comprising a stairstep part in said boundary lineand is to be converted into the multiple-tone pixels;

said third group of patterns being used to detect whether each saidtwo-tone pixel is one comprising said stairstep part in said boundaryline and is to be converted into the multiple-tone pixels;

(d) determining a group priority order such that said step (a) uses agroup from among said first, second and third groups of patterns in thatorder; and

(e) determining a pattern priority order according to which said step(a) uses a pattern from within each group of said first, second andthird groups of patterns.

By applying such a priority order in use of the template patterns,erroneous matching of the template patterns can be prevented.Especially, a certain pixel is prevented from being converted into ahalftone multiple-tone pixel. The certain pixel is a pixel which is notto be converted into a halftone multiple-tone pixel, for example, apixel constituting an end of a straight line in the relevant image. Ifsuch a pixel is converted into a halftone multiple-tone pixel, asharpness in the relevant image may be degraded.

According to another aspect of the present invention, said dot group iscommonly used in said step (b-1) for different magnifications of saidmagnification. As a result, in comparison to a case where a differentgroup of the template patterns is prepared for a differentmagnification, a number of template patterns can be reduced andpreparation of possible duplicate template patterns is eliminated. As aresult, the preparation of the template patterns is easy and thuseconomical.

According to another aspect of the present invention, said step (b-2)divides said dot group into either the single division or the pluralityof divisions in accordance with a relevant magnification of saiddifferent magnifications; and

said dot group comprises a dot pattern such that said tones of saidmultiple tone pixels obtained in said step (b-3) from said dot group aremultiple tones.

For this purpose, said dot group comprises the dot pattern such thatappropriate one of said single division and each of said plurality ofdivisions from said dot group include at least two dots.

Thereby, if any magnifications are applied, each two-tone pixel can beappropriately converted into either a single halftone multiple-tonepixel or a plurality of halftone multiple-tone pixels. As a result, thejaggies in the boundary line are effectively eliminated and thus a fineprinted-out image can be obtained.

According to another aspect of the present invention, different patternsof said dot pattern used in said step (b-1) are prepared for variousmagnifications of said magnification. As a result, it is possible thatif any magnification is applied, a pixel is converted into either singlemultiple-tone pixel or a plurality of multiple-tone pixels, a number ofthe multiple tones being similar even if the magnification is different.Thus, a high-quality printed-out image can be always obtained.

Other objects and further features of the present invention will becomemore apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a block diagram of a digital duplicator having a facsimilefunction in an example of prior art, the present invention being appliedto the duplicator;

FIG. 2 shows magnifications according to which images received throughthe facsimile function are magnified so as to be printed out throughprinters having various resolution capabilities;

FIG. 3 shows a block diagram example of a page printer in an embodimentof the present invention;

FIG. 4 shows a block diagram example of a multiple-tone magnifyingcircuit in the printer shown in FIG. 3;

FIGS. 5A and 5B illustrate a magnifying operation example performed bythe multiple tone magnifying circuit shown in FIG. 4;

FIGS. 6A, 6B, 6C, 6D, and 6E illustrate dot-pattern dividing operationexamples performed after the magnifying operation illustrated in FIGS.5A and 5B;

FIGS. 7A and 7B illustrate another magnifying operation exampleperformed by the multiple-tone magnifying circuit shown in FIG. 4;

FIGS. 8A and 8B illustrate other dot pattern dividing operation examplesperformed after the magnifying operation illustrated in FIGS. 7A and 7B;

FIGS. 9A, 9B, 9C, 9D, and 9E illustrate groups of template patternexamples accompanied by dot pattern examples used in the multiple-tonemagnifying circuit shown in FIG. 4;

FIGS. 10A, 10B, 10C and 10D illustrate a template pattern exampleaccompanied by dot pattern examples particularly prepared for variousmagnifications, which examples may be used in the multiple-tonemagnifying circuit shown in FIG. 4;

FIGS. 11A, 11B, 11C and 11D illustrate a template pattern exampleaccompanied by pixel multiple-tone value examples particularly preparedfor various magnifications, which examples may be used in themultiple-tone magnifying circuit shown in FIG. 4;

FIG. 12 shows a detailed block diagram of an apparatus for processingtwo-tone image data according to the present invention provided in thepage printer shown in FIG. 3 and in the multiple-tone magnifying circuitshown in FIG. 4; and

FIGS. 13A, 13B and 13C illustrate ideal gamma characteristics of arelevant printer, an actual gamma characteristic example thereof, and acorrection characteristic example therefor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A page printer, as a first embodiment of the present invention, havingan apparatus for processing two-tone image data according to the presentinvention and using a method for processing two-tone image dataaccording to the present invention will now be described with referenceto FIG. 3. The page printer shown in FIG. 3 may replace the printer 1shown in FIG. 1.

The page printer receives image data via a modem such as the modem 3shown in FIG. 1. The thus-received image data is data received throughthe facsimile method. The thus-received image data is input to an I/Odevice 12 which is controlled by a CPU 11. The thus-input data is storedin a working RAM 13. The thus-stored data is expanded as a result ofperforming an image reproducing processing on the data, the imagereproducing processing being performed using programs previously storedin a ROM 14. The thus-expanded two-tone image data is stored in a pagememory 15.

In general, an image is transmitted through facsimile transmissionmethod after undergoing run length compression processing, MR, MMR, orthe like. In order to print out the thus-transmitted image, it isnecessary to cause the transmitted data to undergo relevant expansionprocessing, that is, the image reproducing processing.

A printing unit 16 reads the two-tone image data stored in the pagememory 15. The thus-read data is processed by a multiple-tone magnifyingcircuit 17. The circuit 17 thus magnifies, in a predeterminedmagnification (first predetermined magnification such as that determinedthrough the relationship shown in FIG. 2), an image in a form of thetwo-tone image data and converts the two-tone image data tomultiple-tone image data. Thus, a high-quality printing is achieved. Inparticular, the multiple-tone magnifying circuit 17 and a part of theabove-mentioned CPU 11 act as the apparatus for processing two-toneimage data according to the present invention and use the method forprocessing two-tone image data according to the present invention.

With reference to FIG. 4, a structure example of the multiple-tonemagnifying circuit 17 will now be described. An input line buffer unit21 stores two-tone image data representing a plurality of lines ofpixels which include a relevant pixel and pixels surrounding therelevant pixel. A template matching circuit (TPM unit) 22 magnifies therelevant pixel, data of which is stored in the buffer unit 21, in asecond predetermined magnification, with the above-described smoothingoperation being performed on the relevant pixel. The operation executedby the TPM unit 22 will be described later. Thus, a two-tone magnifieddot group is obtained for the relevant pixel. An operating unit 23divides the two-tone magnified dot group in a manner depending on theabove-mentioned first predetermined magnification so as to obtaintwo-tone dot groups. The operating unit 23 performs an averagingoperation on each of the thus-obtained two-tone dot groups. Thus,multiple-tone image data is obtained. The dividing operation andaveraging operation will also be described later.

Output of the operating unit 23, that is, the multiple-tone image data,is stored in an output line buffer unit 24. The buffer unit 24 stores aplurality of lines of pixels in a form of the multiple-tone image data.The thus-stored plurality of lines of pixels are output to the printingunit 16 shown in FIG. 3 in synchronization with pixel clock pulses ofthe printing unit 16.

The multiple-tone magnifying circuit 17 carries out the above-describedoperations in real time between the page memory 15 and the printing unit16.

Algorithm of the operations carried out by the above-describedmultiple-tone magnifying circuit 17 will now be described with referenceto FIGS. 5, 6, 7 and 8.

FIG. 5A shows a pixel arrangement including the relevant pixel and 24pixels surrounding the relevant pixel. The pixel arrangement shown inFIG. 5A is a part of a relevant image represented by an input two-toneimage signal. In the pixel arrangement shown in FIG. 5A, the relevantpixel is represented by a circle having light halftone provided therein,the circle being located at the center of the 25 circles. White pixelsare represented by empty circles and black pixels are represented bycircles having dark halftone provided therein. The representation of thewhite and black pixels will be made in the same manner for otherrelevant figures. Further, representation of white dots and black dotswill also be made in the same manner for other relevant figuresincluding FIG. 5B.

In the algorithm, each of the pixels constituting the relevant image isone by one picked up as being the above-mentioned relevant pixel and,for example, the 24 pixels surrounding the relevant pixel are checked asto how the black pixels and white pixels are arranged. Depending on thethus-checked pixel arrangement of the surrounding pixels and therelevant pixel, the relevant pixel is magnified into a dot groupconsisting of, for example, 12×12 dots, as shown in FIG. 5B. A dot groupsuch as the thus-obtained 12×12 dots may be referred to as theabove-mentioned two-tone magnified dot group. Which number of dots aregiven for the single relevant pixel is determined according to theabove-mentioned second predetermined magnification. The black dot andwhite dot arrangement in the dot group shown in FIG. 5B is determined sothat a shape of a boundary line between the black dots and white dots ofthe dot group is a shape which results from smoothing a shape of aboundary line between the black pixels and white pixels in the blackpixel and white pixel arrangement of the relevant pixel and surroundingpixels shown in FIG. 5A. (The black pixel and white pixel arrangement ofthe relevant pixel and the surrounding pixels will be simply referred toas the pixel arrangement concerning the relevant pixel, hereinafter.Further, the relevant pixel(s) is(are) converted into the dot group(s)so that a shape of a boundary line between the black dot and white dotof the dot group is a shape which results from smoothing a shape of aboundary line between the black pixels and white pixels in the pixelarrangement concerning the relevant pixel will be simply referred to asthe relevant pixel is converted so that an appropriate magnifying andsmoothing operation is performed, hereinafter.) As a result of similarappropriate magnifying and smoothing operation being performed oncontinuous black pixels which constitute the boundary line shown in FIG.5A, overall outline edges of resulting black dot groups are smoothed.(Such an operation as that in which the outline edge is smoothed will bereferred to as `edge correction`, hereinafter.) Thus, the relevant pixelis converted so that an appropriate magnifying and smoothing operationis performed. The above-described operations are carried out by theabove-mentioned TPM unit 22 shown in FIG. 4. How the black dot and whitedot arrangement of the dot group such as that shown in FIG. 5B isobtained through the TPM unit 22 using template patterns will bedescribed later.

Then, the thus-obtained dot group shown in FIG. 5B is divided intodivisions in a manner of manners shown in FIGS. 6A, 6B, 6C, 6D and 6E.Which manner is selected is determined according to the above-mentionedfirst predetermined magnification. FIG. 6A is selected if the firstpredetermined magnification is 1×1, that is, no substantial magnifyingis performed. FIG. 6B is selected if the first predeterminedmagnification is 2×2, that is, twice in the horizontal direction andfurther twice in the vertical direction. FIG. 6C is selected if thefirst predetermined magnification is 2×4, that is, twice in thehorizontal direction and further four times in the vertical direction.FIG. 6D is selected if the first predetermined magnification is 3×3,that is, three times in the horizontal direction and further three timesin the vertical direction. FIG. 6E is selected if the firstpredetermined magnification is 3×6, that is, three times in thehorizontal direction and further six times in the vertical direction.The predetermined magnifications correspond to those shown in FIG. 2.

If the first predetermined magnification is 1×1 as mentioned above, thedot group shown in FIG. 5B is treated as a single pixel and theabove-mentioned averaging operation is performed on the 12×12 dots shownin FIG. 5B. A tone level of the 12×12 dots is standardized on the basisof a predetermined maximum multiple-tone level P. That is, at first, anumber of black dots included in the 12×12 dots is counted. In theexample shown in FIG. 5B, the number of black dots is 42. Theabove-mentioned standardization is performed as shown in the followingequation:

    42(12×12)·P=(7/24)P.

Thus, the (7/24)P tone level is obtained from the 12×12 dots shown inFIG. 5B. Thus, the averaging operation is performed on the two-tonemagnified dot group.

If the first predetermined magnification is 2×2, the 12×12 dots aredivided into 4 divisions, as shown in FIG. 6B, each division consistingof 6×6 dots. The 4 divisions correspond to 4 pixels (2×2 pixels)obtained from the relevant pixel shown in FIG. 5A. The averagingoperation is performed on each of the 4 divisions as follows: The numberof black dots included in each of the 4 divisions is 0, 0, 12 and 30.Then, the averaging operation is performed as shown in the followingequations:

    0/(6×6)·P=0;

    0/(6×6)·P=0;

    12/(6×6)·P=(1/3)P; and

    30/(6×6)·P=(5/6)P.

Thus, the resulting 2×2 pixels have multiple-tone levels of 0, 0, (1/3)Pand (5/6)P, respectively.

Similarly, if the predetermined first magnification is one of 2×4, 3×3,and 3×3, the 12×12 dot group shown in FIG. 5B is divided into a relevantone of 8 divisions, 9 divisions and 18 divisions, as shown in FIGS. 6C,6D and 6E. In each case, each division consists of a relevant one of 6×3dots, 4×4 dots and 4×2 dots, as shown in the figures. In each case, theaveraging operation is performed on each of the divisions.

The above-described dividing and averaging operations are carried out bythe above-mentioned operating unit 23 shown in FIG. 4.

Further, if the first predetermined magnification is not an integer x aninteger, that is, if the magnification is, for example, 1.5×1.5 or1.5×3, the following method may be applied: The TPM unit 22 treats 4(2×2) adjacent pixels as relevant pixels at the same time, as shown inFIG. 7A. The 4 relevant pixels are magnified to the dot group of 6×6dots shown in FIG. 7B. The black dot and white dot arrangement of thedot group shown in FIG. 7B is determined so that the 4 relevant pixelsare converted so that an appropriate magnifying and smoothing operationis performed.

Then, the operating unit 23 divides the thus-obtained dot group shown inFIG. 7B into 9 divisions, each division consisting of 2×2 dots, as shownin FIG. 8A, in the case the magnification is 1.5×1.5; or into 18divisions, each division consisting of 2×1 dots, as shown in FIG. 8B, inthe case the magnification is 1.5×3. Thus, the 2×2 relevant pixels aremagnified into 9 (3×3) in the former case. Thus, a number of pixels isincreased 1.5×1.5 times. Similarly, the 2×2 relevant pixels aremagnified into 18 (3×6) in the latter case. Thus, a number of pixels isincreased 1.5×3 times. In each case, the operating unit 23 performs theaveraging operation on each division. Thus, the multiple-tone levels areobtained for a number of pixels which have been obtained as a result ofmagnifying in the first predetermined magnification.

How the black dot and white dot arrangement of the dot group such asthat shown in FIG. 5B is obtained through the TPM unit 22 using templatepatterns will now be described. The dot group is obtained as a result ofdetermining which of previously stored template patterns matches thepixel arrangement concerning the relevant pixel such as that shown inFIG. 5A.

FIGS. 9A, 9B, 9C, 9D and 9E show 5 groups of the above-mentionedtemplate patterns TP in an example. Each template pattern of thetemplate patterns TP consists of 5×5 pixels as shown in the figures. Ineach template pattern TP, a pixel located at the exact center in the 5×5pixels is the above-mentioned relevant pixel as that shown in FIG. 5A.The 5 groups of template patterns TP are previously stored in a memoryof the TPM unit 22. Dot patterns DP shown in FIGS. 9A, 9B, 9C. 9D and 9Eare used to obtain a two-tone magnified dot group such as that shown inFIG. 5B for the relevant pixel from the black pixel and white pixelarrangement of the relevant pixel and the surrounding pixels such asthat shown in FIG. 5A. Each pattern of the dot patterns DP consists of8×8 dots while the dot group shown in FIG. 5B consists of 12×12 dots.Such difference in dot formations does not matter but is merely due todesign choice. If a pattern of the template patterns TP is determined asmatching the pixel arrangement concerning the relevant pixel, a dotpattern, among the dot patterns DP, accompanying the thus-determinedtemplate pattern in FIGS. 9A-9E is determined to be the two-tonemagnified dot group for the relevant pixel.

In each of the template patterns TP shown in FIGS. 9A, 9B, 9C, 9D, and9E, each empty circle represents a white pixel; each circle having darkhalftone provided therein represents a black pixel; and each circlehaving light halftone provided therein represents a pixel which may beeither a black pixel or a white pixel, that is, a pixel of DON'T CARE.

The above-described groups of template patterns shown in FIGS. 9A-9Econsist of a group 1 shown in FIG. 9A, a group 2 shown in FIG. 9B, agroup 3 shown in FIG. 9C, a group 4 shown in FIG. 9D and a group 5 shownin FIG. 9E. The group 1 template pattern TP is used to detect a relevantpixel which is not to be converted into a multiple-tone pixel eventhrough the multiple-tone magnifying circuit 17 shown in FIG. 4. Such arelevant pixel is, for example, a pixel whereby a possibility of thepixel constituting a vertex of an angular end of a straight line havinga thickness in a relevant image is high.

The groups 2, 3, 4 and 5 of the template patterns TP are used to detecta relevant pixel which is to be converted into a multiple-tone pixelthrough the multiple-tone magnifying circuit 17. Further, the group 2template patterns TP are used to detect a relevant pixel whereby apossibility of the pixel not constituting a stairstep part in therelevant image is high. Such a relevant pixel is a pixel, a possibilityof the pixel constituting, for example, an intermediate part of anoblique line in the relevant image, or a vertex of an acute angleoutline in the relevant image, is high. A basic stairstep part comprisesa first part extending along the scan line direction; a second partextending, from an extending end of the first part, alongperpendicularly to the scan line direction; and a third part extending,from an extending end of the second part, along the scan line direction.The oblique line is a line extending obliquely to the scan linedirection.

The groups 3, 4, 5 of the template patterns TP are used to detect arelevant pixel whereby a possibility of the pixel constituting thestairstep part in the relevant image is high. The group 3 templatepatterns TP are used to detect either a black pixel or a white pixelconstituting the stairstep part which has a step interval of 3 pixels.The step interval is a number of pixels straightly arranged between twoadjacent step changes. The group 4 template patterns TP are used todetect either a black pixel or a white pixel constituting the stairsteppart which has a step interval of 2 pixels. The group 5 templatepatterns TP are used to detect either a black pixel or a white pixelconstituting the stairstep part which has a step interval of one pixel.

The memory of the TPM unit 22 storing the above-described groups of thetemplate patterns TP and dot patterns DP may also store other templatepatterns with accompanying dot patterns. The other patterns are obtainedas a result of left and right reflections, top and bottom reflections,left and right and also top and bottom reflections of the patterns. Theother patterns may also include patterns other than those mentionedabove.

A priority order is predetermined among the above-mentioned 5 groups 1,2, 3, 4 and 5 of the template patterns TP shown in FIGS. 9A through 9E.The priority order is an order according to which group of the 5 groupsis used in determining whether or not the template patterns TP of thegroup match the pixel arrangement concerning the relevant pixelrepresented by the input two-tone image signal. The priority order is anorder in which a group having a smaller group number is used earlierthan a group having a larger group number. That is, the group 1 templatepattern TP is used first and the group 5 template patterns TP are usedlast.

Further, a similar priority order is predetermined within templatepatterns TP belonging to each group of the 5 groups. Therefore, if it isdetermined that each of a plurality of template patterns TP matches thepixel arrangement of the input two-tone image signal, it is possible toselect one template pattern from among the plurality of templatepatterns. Thus, in such a situation that each of the plurality oftemplate patterns matches the pixel arrangement of the input two-toneimage signal, an operation of the selection of a single template patternfrom among the 5 groups of template patterns is not at a deadlock.

There may be a case where, in the above-described embodiment of thepresent invention, that the template pattern TP of the group 1, to whichthe highest priority order is assigned, matches the pixel arrangement ofthe input two-tone image signal. In such a case, it is highly possiblethat a relevant pixel is a pixel constituting a vertex of an angular endof a straight line in a relevant image. In such a case, the smoothingand magnifying operation is performed as shown in FIG. 9A. Thus, in theresulting dot pattern DP shown in FIG. 9A, all dots of the 8×8 dots areblack dots.

In such a case, the above-described averaging operation is performed onthe dot pattern DP through the operating unit 23. However, since all thedots are black dots as mentioned above, the maximum tone level isobtained as a result of performing the averaging operation. Theaveraging operation may be performed on whole 8×8 dot pattern DP.Instead, the averaging operation may be performed on each of dotpatterns obtained as a result of dividing, as shown in FIGS. 6B-6E, theabove-mentioned 8×8 dot pattern DP. The above-mentioned dividingoperation is performed according to an appropriate magnification such asthat shown in FIG. 2. However, in each case, since all the dotsconstituting the dot pattern DP are black dots, the averaging operationresults in the maximum tone levels (the above-mentioned maximummultiple-tone level P of the relevant printer). Thus, in such a case,the tone of the relevant pixel is not converted into a middle tone amongthe multiple tones. That is, no substantial edge correction as describedabove is performed on the relevant pixel. As a result, sharpness of avertex of an angular end of a straight line in a relevant image isprevented from being degraded. The sharpness degradation may occur if atone of such a relevant pixel was converted into a middle tone among themultiple tones.

Further, the group 2 template patterns TP shown in FIG. 9B includestemplate patterns which may match the pixel arrangement of the inputtwo-tone image signal having the relevant pixel constituting a vertex ofan angular end, that is, which template patterns TP may detect a vertexof an angular end. For example, the top leftmost template pattern amongthose shown in FIG. 9B may detect a vertex of an angular end. As aresult, it may be that the relevant pixel constituting a vertex of anangular end is detected by the group 1 template pattern TP and also isdetected by some of the group template patterns TP. However, the group 1has the priority order higher than that of the group 2 as mentionedabove. Therefore, the smoothing and magnifying operation according tothe group 2 shown in FIG. 9B may be performed only on the relevantpixels, the pixel arrangements of which relevant pixels do not match thetemplate pattern TP of the group 1. Further, the relevant pixel detectedby the group 1 template pattern TP is surely prevented from undergoingthe edge correction operation. As shown in FIG. 9B, each of the dotpatterns DP includes white dots. Therefore, the smoothing and magnifyingoperation according to the group 2 constitutes the edge correctionoperation.

The dot patterns DP accompanying the template patterns TP belonging tothe group 2 shown in FIG. 9B are suitable for appropriately performingthe smoothing and magnifying operation on the relevant pixelsconstituting an end point of a 450 oblique line, or a vertex of an acuteangle pattern in the horizontal direction which is a vertex projectinghorizontally, or a vertex of an acute angle pattern in the verticaldirection which is a vertex projecting vertically, in the relevantimage. The bottom leftmost template pattern among those shown in FIG. 9Bis one for detecting a pixel constituting a vertex of an acute anglepattern in the horizontal direction. The top rightmost template patternamong those shown in FIG. 9B is one for detecting a pixel constituting avertex of an acute angle pattern in the vertical direction.

The template patterns TP belonging to the groups 3, 4 and 5 shown inFIGS. 9C, 9D and 9E are those which are used to detect pixelsconstituting the stairstep part. The lower priority order is assigned tothe template pattern TP which is used to detect a pixel constituting thestairstep part having a step interval of a smaller number of pixels. Thehigher priority order is assigned to the template pattern TP which isused to detect a pixel constituting the stairstep part having a stepinterval of a larger number of pixels. By such assignment of thepriority orders, erroneous stairstep part detection can be easilyprevented. The dot patterns DP accompanying the template patterns TPbelonging to the groups 3, 4 and 5 shown in FIGS. 9C, 9D and 9D aresuitable for appropriately performing the smoothing and magnifyingoperation on the relevant pixels constituting the stairstep parts.

Why erroneous stairstep part detection can be easily prevented asmentioned above will now be described. It may be that a same imagepattern is be detected using, for example, the top leftmost templatepattern of those shown in FIG. 9D, which is used to detect two pixelinterval stairstep parts, and also detected using, for example, the topmiddle template pattern of those shown in FIG. 9C, which is used todetect three pixel interval stairstep parts. In this example case, imagepatterns which are detected using the top leftmost template pattern inFIG. 9D include all of image patterns which are detected using the topmiddle template pattern in FIG. 9C. Therefore, if the priority of thetop leftmost pattern of FIG. 9D were higher than the top middle patternof FIG. 9C, no image pattern would remain after the top leftmost patternof FIG. 9D is used to detect image patterns. As a result, three pixelinterval stairstep parts could not be detected. In order to eliminatesuch a problem, it is possible to design template patterns such thatthere is no possibility of arising of such a problem. However, if suchtemplate patterns were designed, a number of template patterns should beincreased, thus being problematic. By simply making higher a priority oftemplate patterns for detecting shorter pixel interval stairstep parts,the problem can be eliminated. The eliminated problem is one that longerpixel interval stairstep parts could not be detected.

These template patterns TP used by the TPM unit 22 and the dot patternsDP used by the operating unit 23 can be used in common for all themagnifications which the relevant system requires as shown in FIG. 2.

In this case, a relevant dot pattern DP of the dot patterns DP shown inFIGS. 9A-9E is divided according to a relevant magnification. Thedividing of a dot pattern according to a relevant magnification isperformed as shown in FIGS. 6B, 6C, 6D and 6E. There is a conditionthat, after the dividing, each pixel including an edge part of arelevant image has to be converted into a middle tone of the multipletones. The above-mentioned edge part is a part in which black dots comeinto contact with white dots at a stairstep boundary line. Each pixelafter the dividing is a pixel consisting of a relevant division of thedot pattern. In the example of FIGS. 9B-9E, a maximum possible dividingwhich fulfills the above-mentioned condition is at least dividing suchthat each division consists of 2×2 dots as shown in the drawings. Each2×2 dot group constitutes a pixel after the dividing.

However, in another structure example of the multiple-tone magnifyingcircuit 17, dot patterns DP are not commonly used for all themagnifications but a different dot pattern is prepared for eachmagnification as shown in FIGS. 10A-10D. The dot patterns DP shown inFIGS. 10B, 10C and 10D are prepared for the template pattern TP shown inFIG. 10A. Further, the dot patterns DP shown in FIGS. 10B, 10C and 10Dare prepared for magnifications of 1×1, 2×2 and 2×4, respectively. Themagnification 1×1 means no substantial magnifying is performed. In FIG.10A, the relevant pixel in the pixel arrangement concerning the relevantpixel is indicated as a center circle having light halftone providedtherein. This indication is also applied to FIG. 11A.

When a magnification to be used is determined among the magnifications,for example, 1×1, 2×2 or 2×4, as mentioned above, only dot patternsrelevant to the thus-determined magnification are stored in a memory ofthe operating unit 23 so that a relevant dot pattern DP stored thereincan be read out for each template pattern TP. The thus-stored relevantdot patterns are obtained as a result of being transferred bymultiple-tone data transfer means 29 which will be described later.

Such a first system in which different dot patterns DP are prepared forvarious magnifications will now be compared with a second system inwhich a common dot pattern DP is used for various magnifications asmentioned above. For the first system, extra design works and costs aredisadvantageously required to prepare the different dot patterns DP.However, it is possible to maintain a number of dots constituting apixel obtained through the smoothing and magnifying operation, to benumbers not less than a predetermined value. In the example of FIGS.10A, 10B, 10C, and 10D, the number of dots constituting the pixel is 9for each of the magnifications 1×1 and 2×2, as shown in FIGS. 10B, 10C,and 6 for the magnification 2×4 as shown in FIG. 10D. Thus, the pixelcan be a halftone or middle tone multiple-tone pixel appropriately andthus a tone level of the pixel can be finely controlled. Further, ahigh-quality image can be obtained through converting the two-tone imageinto the multiple-tone image.

Instead of preparing the different dot patterns DP for variousmagnifications, it is also possible that a different tone value of apixel be specially prepared for a each magnification as shown in FIGS.11B-11D. Each of the above-mentioned dot patterns DP or tone values of apixel will be generally named `smoothly magnified pixel data`.

In this case, the smoothing and magnifying operation includes theaveraging operation. If the template pattern TP is determined for thepixel arrangement concerning the relevant pixel, tone valuesaccompanying the thus-determined template pattern TP are determined forthe relevant pixel. The thus-determined tone values are those preparedfor the relevant magnification. If the template pattern TP shown in FIG.11A (the same as that shown in FIG. 10A) is determined to match thepixel arrangement concerning the relevant pixel, the tone value shown inFIG. 11B is determined for a pixel which serves as a pixel obtained as aresult of performing the smoothing, magnifying and averaging operationon the relevant pixel for the magnification 1×1. Similarly, the tonevalues shown in FIG. 11C are determined for four pixels which serve aspixels obtained as a result of performing the smoothing, magnifying andaveraging operation on the relevant pixel for the magnification 2×2. Thetone values shown in FIG. 11D are determined for eight pixels whichserve as pixels obtained as a result of performing the smoothing,magnifying and averaging operation on the relevant pixel for themagnification 2×4.

The tone values shown in FIGS. 11B and 11C correspond to the dotpatterns DP shown in FIGS. 10B and 10C, respectively. Further, the tonevalues shown in FIGS. 11B and 11C are equal to those which are obtainedas a result of the averaging operation being performed on the dotpatterns DP shown in FIGS. 10B and 10C, respectively. In fact, forexample, the bottom right division of the dot pattern DP shown in FIG.10C consists of 9 dots including 7 black dots. Correspondingly, thebottom right tone value in the four tone values shown in FIG. 11C is(7/9) P.

As shown in FIG. 10D and FIG. 11D, in this embodiment, each division ofthe dot pattern DP shown in FIG. 10D consists of 6 dots, while each tonevalue of the tone values shown in FIG. 11D is (A/9)P, where "A" may beone of 10 numbers, 0 through 9. Therefore, the dot pattern DP shown inFIG. 10D does not exactly correspond to the tone value shown in FIG. 11Dand thus the tone value shown in FIG. 11D is not equal to one is whichis obtained as a result of the averaging operation being performed onthe dot pattern DP shown in FIG. 10D. However, it is also possible thatthe dot pattern DP shown in FIG. 10D is modified so that each divisionof the dot pattern consists of 9 dots. If this modification isperformed, it is possible that the resulting dot pattern DP may exactlycorrespond to the tone value shown in FIG. 11D and thus the tone valueshown in FIG. 11D may be equal to one which is obtained as a result ofthe averaging operation being performed on the resulting dot patternsDP.

When a magnification to be used is determined among the magnifications,for example, 1×1, 2×2 or 2×4, as mentioned above, only tone valuesrelevant to the thus-determined magnification are stored in a memory ofthe operating unit 23 so that relevant tone values stored therein can beread out for each template pattern TP. The thus-stored tone values areobtained as a result of being transferred by the above-mentionedmultiple tone data transfer means 29.

The above-mentioned apparatus for processing two-tone image dataaccording to the present invention in the page printer, which wasdescribed with reference to FIGS. 3 and 4, will now be described indetail with reference to FIGS. 3 and 12.

The template matching unit 22 includes a 5×5 pixel latch unit 25 and a5×5 pixel TPM unit 26. The 5×5 pixel latch unit 25 obtains the two-toneimage data from the page memory 15 shown in FIG. 3. The two-tone imagedata was obtained based on image data which was received through afacsimile function of a system such as that shown in FIG. 1. The 5×5pixel latch unit 25 maintains 5×5 pixels of the two-tone image data atthe same time. The 5×5 pixels are those which correspond to theabove-mentioned pixel arrangement concerning the relevant pixel. In theunit 25, the 5×5 pixels are changed so that the relevant pixel ischanged one by one in response to the obtaining of the two-tone imagedata. The 5×5 pixel TPM unit 26 uses various template patterns TP suchas those shown in FIGS. 9A through 9F, to determine whether or not oneof the template patterns TP matches the pixel arrangement of the 5×5pixels maintained in the 5×5 pixel latch unit 25.

The operating unit 23 includes a RAM 27 as shown in FIG. 12. The RAM 27is the above-mentioned memory which stores the above-mentioned smoothlymagnified pixel data. In addition to the RAM 27, appropriate elementssuch as adders and other operating elements are included in theoperating unit 23, even though they are not shown in the figure. Thus,the operating unit 23 operates as described above.

The ROM 14, which is shown not only in FIG. 12 but also in FIG. 3,stores not only operating programs for the operation of the CPU 11 butalso the above-mentioned smoothly magnified pixel data. The smoothlymagnified pixel data stored in the ROM 14 includes various kinds ofsmoothly magnified pixel data which are different for variousmagnifications such as those shown in FIG. 2. The smoothly magnifiedpixel data may consist of either dot patterns DP such as those shown inFIGS. 10B through 10D or multiple-tone data such as those shown in FIGS.11B through 11D.

Functions of the CPU 11, also shown in FIG. 3, include functions ofmagnification calculating means 28, the above-mentioned multiple-tonedata transfer means 29, and multiple-tone data correction means 30 asshown in FIG. 12.

The magnification calculating means 28 selects a magnification fromamong the magnifications shown in FIG. 2. The selection is performedeach time when a new series of image data is received through thefacsimile function and input to the I/O device 12 shown in FIG. 3. Theselection is performed as follows: A type of a facsimile apparatus whichtransmits the image data to the relevant system is determined. Further,which transmission resolution mode is used by the transmitting apparatusamong modes such as an ordinary-resolution transmission mode and afine-resolution transmission mode is determined. The fine-resolutiontransmission mode is, for example, a mode resulting in a facsimiletransmission image having a resolution of 8×7.7 shown in FIG. 2. Theordinary-resolution transmission mode is, for example, a mode resultingin a facsimile transmission image having a resolution of 8×3.85 shown inFIG. 2. A super-fine-resolution transmission mode is, for example, amode resulting in a facsimile transmission image having a resolution of16×16 shown in FIG. 2. The determination is performed based on pixeldensity of the received image data. The above-mentioned selection isperformed using the result of the above-mentioned determination and theresolution of the printer to be used in printing out the relevant image.

The multiple-tone data transfer means 29 reads the smoothly magnifiedpixel data from the ROM 14, which data was prepared for themagnification selected by the magnification calculating means 28. Thetransfer means 29 transfers the thus-read smoothly magnified pixel datato the multiple-tone correction means 30. The correction means 30corrects the transferred smoothly magnified pixel data which data isthen stored in the RAM 27 in the operating unit 23.

The correction of the correction means 30 is performed so as to obtain aprinted-out image which has desired characteristics corresponding tothose of the image data which is received through the facsimilefunction. The characteristics of the image data received through thefacsimile function may be adversely affected by gamma characteristics ofthe relevant printer and so forth. This correction is performed based onthe gamma characteristics of the relevant printer, environment variationsuch as ambient temperature variation, characteristics variation of aphotosensitive substance drum and so forth in the printer due to agingthereof. In the present embodiment shown in FIG. 12, a test patternreading unit 31 supplies data which is then used for the correction. Thecorrection using the data from the test pattern reading unit 31 will bedescribed later.

A number of the template patterns TP used by the TPM unit 26 fordetermining matching of them with the relevant pixel arrangement will bereferred to as TPN, hereinafter. A comparison example of a structure ofthe operating unit 23 different from that of the operating unit 23 inthe embodiment according to the present invention will now be consideredfor comparison. In the comparison example, a ROM is used instead of theRAM 27 shown in FIG. 12 to store all kinds of the smoothly magnifiedpixel data different for all possible magnifications for the printerresolution of 400 dpi shown in FIG. 2. The smoothly magnified pixel datais such as that shown in FIGS. 11B, 11C and 11D. In this comparisonexample, a required capacity of the RON is calculated as follows:

For the 1×1 magnification, a capacity of 68TPN bits, calculated byTPN×(1×1)×8=8TPN, is required;

similarly, for the 2×2 magnification, a capacity of 32TPN bits,calculated by TPN×(2×2)×8 =32TPN, is required; and

for the 2×4 magnification, a capacity of 64TPN bits, calculated byTPN×(2×4)×8 =64TPN, is required.

As a result, a total capacity of 104TPN bits is required for the ROM. Inthe above calculations, it is assumed that the data amount of 8 bits isused for each pixel which serves as a pixel obtained as a result ofperforming the smoothing, magnifying and averaging operation on therelevant pixel for a relevant magnification of those of 1×1, 2×2 and2×4. Therefore, the number 8 is multiplied by a respective magnificationof those 1×1 as shown in FIG. 11B, 2×2 as shown in FIG. 11C and 2×4 asshown in FIG. 11D in each calculation.

A case is assumed for each pixel which serves as the pixel obtained as aresult of performing the smoothing, magnifying and averaging operationon the relevant pixel for a relevant magnification of those of 1×1, 2×2and 2×4. In this case, a total number of tones is 10, which tonesconsisting of values 0, (1/9)P, . . . . , (1/9)P as shown in FIGS. 11B,11C and 11D. However an ordinary laser printer has a capability ofexpressing 256 multiple tones. It is necessary to supply multiple-toneimage data to such a printer, which data matches the capability of theprinter. Therefore, it is necessary to provide the capacity of theabove-mentioned ROM determined based on the matter that the data amountof 8 bits is used for each pixel which serves as the pixel obtained as aresult of performing the smoothing, magnifying and averaging operationon the relevant pixel for a relevant magnification of those of 1×1, 2×2and 233 4. In this case, it may be that only 10 tones are used among the256 tones actually.

The above case is based on 9 dots or 6 dots being used to represent eachpixel which serves as the pixel obtained as a result of performing thesmoothing, magnifying and averaging operation on the relevant pixel fora relevant magnification of those of 1×1, 2×2 and 2×4 as shown in FIGS.10B, 10C and 10D. However, in order to advantageously reduce capacitiesof relevant memories, it is also possible that only two dots are used torepresent each pixel which serves as the pixel obtained as a result ofperforming the smoothing, magnifying and averaging operation on therelevant pixel for a relevant magnification of those of 1×1, 2×2 and2×4. In this case, 3 multiple tones are used for each pixel.

However, in the present embodiment shown in FIG. 12, in contrast to theabove-descried comparison example, a RAM such as the RAM 27 is usedinstead of the ROM in the operating unit 23. Thereby, a capacity of only64TPN bits is required for the RAM 27, since the maximum capacity isthat of 64TPN bits among capacities of 8TPN bits, 32TPN bits and 64TPNbits possible for the magnifications of 1×1, 2×2 and 2×4. Thus, incontrast to the capacity of 104TPN required for the ROM of thecomparison example, the capacity of the RAM 27 can be reduced. Thus, acapacity of a memory for storing the smoothly magnified pixel data isreduced. In the embodiment shown in FIG. 12, as described above, thesmoothly magnified, pixel data prepared for the relevant magnificationis transferred from the ROM 14 to the RAM 27, a download process beingthus performed. This download process is performed each time when themagnification calculating means 28 determines the relevant magnificationas a new magnification as described above. As a result of this reductionof the capacity of the memory for storing the smoothly magnified pixeldata, the template matching unit 22 and operating unit 23 can bemanufactured economically if they are manufactured as a semiconductorchip of an ASIC.

However, it is also possible that, as the above-described comparisonexample, a ROM is used instead of the RAM 27 shown in FIG. 12 topreviously store all kinds of the smoothly magnified pixel datadifferent for all possible magnifications for the printer resolution of400 dpi shown in FIG. 2. A smoothly magnified pixel data may beselected, from the thus-stored data, relevant to a particularmagnification of the facsimile received data.

Further, the 2×2 magnification is ordinarily used as a standardmagnification. Therefore, it is possible that a certain transferoperation is automatically performed immediately after a power is turnedON in the relevant system. The certain transfer operation is that inwhich the smoothly magnified pixel data prepared for the magnificationof 2×2 is transferred to the RAM 27 so as to be default data. Only ifthe magnification calculating unit 28 determines the magnificationdifferent from the magnification of 2×2, the smoothly magnified pixeldata prepared for different magnification is transferred to the RAM 27.

Further, the smoothly magnified pixel data is produced on the assumptionthat a relevant printer which prints out an image using the smoothlymagnified pixel data has gamma characteristics such as that shown inFIG. 13A which are linear. That is, a relationship between tones ofinput image data and tones of a printed-out image are linear. However,an actual printer has different gamma characteristics such as that shownin FIG. 13B. According to the gamma characteristics shown in FIG. 13B,desired tones may not be obtained, that is, tone levels are undesirablylow in a part of the printed-out image in which tone levels arerelatively low. Thus, desired tones may not be obtained in theprinted-out image.

In the embodiment shown in FIG. 12, it is possible that themultiple-tone data correction means 30 corrects the smoothly magnifiedpixel data so that the adverse effects due to the difference in thegamma characteristics of the relevant printer such as that between FIG.13A and FIG. 13B can be eliminated. Thus, the desired tones may beobtained in the printed-out image. For this purpose, the multiple-tonedata correction unit 30 performs correction such as that shown in FIG.13C on the smoothly magnified pixel data and the resulting data isstored in the RAM 27.

Further, it is also possible in the embodiment shown in FIG. 12 thatactual performance in the relevant printer is detected and thus used bythe multiple-tone pixel data correction means 30 to correct the smoothlymagnified pixel data. For this purpose, a certain part of aphotosensitive substance drum of the relevant printer is used. Thecertain part of the photosensitive substance drum is an extra part whichis not used in an ordinary printing operation. In each printingoperation, all expressible tones, for example, 256 tones are formed as atone test pattern in the certain part of the photosensitive substancebody. The thus-formed test pattern is read by the test pattern readingunit 31 shown in FIG. 12. Thus, the actual performance of the relevantprinter can be detected. Using the thus-detected actual performance, themultiple-tone data correction means 30 automatically corrects thesmoothly magnified pixel data to be stored in the RAM 27.

A method such as that in which the actual performance such as actualgamma characteristics is detected by using the read test pattern asdescribed above was performed in a conventional laser printer.Therefore, a detail description of the method is omitted.

Further, it is also possible that environment variation such astemperature and/or humidity variation in the relevant printer isdetected. The multiple-tone data correction means 30 uses the result ofthe detection and thus corrects the smoothly magnified pixel data.Further, it is also possible that an operator may input data to therelevant system through a plurality of touch switches provided on anoperation panel of the system. Specifically, for example, the operatormay input a specification in which tone levels obtained in theprinted-out image can be arbitrarily changed. For example, all tonelevels can be shifted, or only tone levels of either a high-level zoneor a low-level zone of the all tone levels can be shifted.

Applications of the present invention are not limited to the pageprinter of the digital duplicator having the facsimile function such asthat described above. The present invention can also be applied to otherfacsimile apparatuses and other image forming apparatuses havingfacsimile functions. The present invention can further be applied to animage display apparatus such as that using a CRT.

Further, the present invention is not limited to the above-describedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. An image forming apparatus for processingtwo-tone image data so as to convert each two-tone pixel constituting arelevant image into a plurality of pixels and smooth a boundary linebetween a zone consisting of first-tone pixels of two-tone pixelsconstituting said relevant image and a zone consisting of second-tonepixels of said two-tone pixels,said apparatus comprising: means which,for each two-tone pixel of said two-tone pixels, determines a templatepattern, from among a plurality of template patterns, as matching apixel arrangement comprising pixels located around said each two-tonepixel; means for converting said each two-tone pixel into either asingle multiple-tone pixel or a plurality of multiple-tone pixels, saidmeans using a result of the determination performed by said means forthe converting; and image forming means for forming an image on arecording medium based on conversion result of said converting means. 2.The apparatus according to claim 1, further comprising:means fordetermining a ratio according to which said apparatus converts saidtwo-tone pixels constituting said relevant image; said means, fordetermining the ratio using image data which is received through afacsimile function and is used to obtain said two-tone image data. 3.The apparatus according to claim 2, further comprising:means fortransferring smoothly converting pixel data to said means, which data ispreviously prepared for said conversion and is used for converting saideach two-tone pixel into either said single multiple-tone pixel or saidplurality of multiple-tone pixel in said means.
 4. The apparatusaccording to claim 3, further comprising:means for correcting saidsmoothly converted pixel data so as to eliminate a difference betweenideal printing-out characteristics and actual printing-outcharacteristics.
 5. An image forming method for processing two-toneimage data so as to converting each two-tone pixel constituting arelevant image into a plurality of pixels and smooth a boundary linebetween a zone consisting of first-tone pixels of two-tone pixelsconstituting said relevant image and a zone consisting of second-tonepixels of said two-tone pixels.said method comprising steps of: (a)determining, for each two-tone pixel of said two-tone pixels, a templatepattern, from among a plurality of template patterns, as matching apixel arrangement comprising pixels located around said each two-tonepixel; (b) converting said each two-tone pixel into either a singlemultiple-tone pixel or a plurality of multiple-tone pixels, said step(b) using a result of the determination performed by said step (a) forthe converting and (c) forming an image on a recording medium based onconversion result of said step (b).
 6. The method according to claim 5,wherein:said step (b) further comprises steps of: (b-1) converting saidtwo-tone each two-tone pixel into a two-tone dot group; (b-2) dividingsaid dot group into either a single division or a plurality ofdivisions; and (b-3) averaging tones of dots constituting appropriateone of said single division or said plurality of divisions, a result ofthe averaging constituting either a tone of said single multiple-tonepixel or tones of said plurality of multiple-tone pixels.
 7. The methodaccording to claim 6, wherein:said method further comprises steps of:(c) classifying said plurality of template patterns into a first groupof patterns, a second group of patterns and a third group of patterns;said first group of patterns being used to detect whether said eachtwo-tone pixel is to be converted into either said single multiple-tonepixel or said plurality of multiple-tone pixels; said second group ofpatterns being used to detect whether said each two-tone pixel is onecomprising a stairstep part in said boundary line and is to be convertedinto either said single multiple-tone pixel or said plurality ofmultiple-tone pixels; said third group of patterns being used to detectwhether said each two-tone pixel is one comprising said stairstep partin said boundary line and is to be converted into either said singlemultiple-tone pixel or said plurality of multiple-tone pixels; (d)determining a group priority order such that said step (a) uses a groupfrom among said first, second and third groups of patterns in thatorder; and (e) determining a pattern priority order according to whichsaid step (a) uses a pattern from within each group of said first,second and third groups of patterns.
 8. The method according to claim 6,wherein said two-tone dot group is commonly used in said step (b-1) fordifferent ratios of said conversion.
 9. The method according to claim 8,wherein:said step (b-2) divides said two-tone dot group into either saidsingle division or said plurality of divisions in accordance with arelevant ratio of said different ratios; and said two-tone dot groupcomprises a dot pattern such that each tone of either said tone of saidsingle multiple-tone pixel or said tone of said plurality ofmultiple-tone pixels obtained in step (b-3) from said two-tone dot groupis a multiple tone.
 10. The method according to claim 9, wherein, ifeach two-tone pixel of either said single multiple-tone pixel or saidplurality of multiple-tone pixels is a pixel comprising a stairstep partof said boundary line, a tone of said each pixel is a middle tone. 11.The method according to claim 9, wherein said two-tone dot groupcomprises said dot pattern such that appropriate one of said singledivision and each of said plurality of divisions from said two-tone dotgroup includes at least two dots.
 12. The method according to claim 6,wherein:different patterns of said two-tone dot group used in said step(b-1) are prepared for various ratios of said conversion.
 13. The methodaccording to claim 6, wherein:said step (b) further comprises a step of:(b-4) determining each tone of either said single multiple-tone pixels,which tone is different for various ratios of said conversion for eachtemplate pattern of said plurality of template patterns.
 14. The methodaccording to claim 13, wherein:said method further comprises steps of:(c) classifying said plurality of template patterns into a first groupof patterns, a second group of patterns and a third group of a patterns;said first group of patterns being used to detect whether said eachtwo-tone pixel is to be converted into said single multiple-tone pixelor said plurality of multiple-tone pixels; said second group of patternsbeing used to detect whether said each two-tone pixel is one comprisinga stairstep part in said boundary line and is to be converted into saidsingle multiple-tone pixel or said plurality of multiple-tone pixels;said third group of patterns being used to detect whether said each twotone pixel is one comprising said stairstep part in said boundary lineand is to be converted into either said single multiple-tone pixel orsaid plurality of multiple-tone pixels; (d) determining a group priorityorder such that said step (a) uses a group from among said first, secondand third groups of patterns in that order; and (e) determining priorityorder according to which said step (a) uses a pattern from within eachgroup of said first, second and third groups of patterns.